ghc821: init at 8.2.1-rc2 (a.k.a., 8.2.0.20170507)

The approach taken to add this package was to port over the definitions
currently existing for HEAD, and making the necessesary changes to get
this building.

The Haskell package set associated with this compiler doesn't yet
guarantee that all or most of the packages successfully build with this
new compiler, but that will improve over time after this GHC 8.2.1
is officially released and the ecosystem catches up.